While the focus for some will be on things like Google's VR efforts, called Daydream, and their newly announced smart speaker called Google Home, it shouldn't be forgotten that Google I/O is a developer conference and as such will have a lot to do with software and things that make life easier on developers. Beta apps on Android are not new and the Play Store actually holds tons of beta applications, but finding and installing these is not always easy. Google is setting things up to change as they have announced a new simpler form of discovering beta apps on Google Play.
It's called Google Play Early Access, and as the name suggests this will be a way for users to more easily find apps that have been launched but are currently in beta status. Prior to the early access platform inside of the Play Store, users would have to opt into the beta through a specialized link that generally comes from the app developers. Once they've joined the beta the app becomes visible to them and is available to download and install on their chosen devices. With Google Play Early Access, there will be a new section within the Play Store that users will be able to enter and find any apps that they want to be a beta tester for, and be able to join from with the app or the Google Play website. Google does note that the apps listed in this section will be "hand-picked" so not all open beta apps will show up there.
This won't be any different from the rest of the sections as Google curates top apps lists and such as well, so the Early Access section will be a curated grouping of those which are the most promising. In addition to the new Early Access sections, apps that are in an open beta status but not in production yet will start to show up in Play Store search results, making it easy for users to find these apps if they happen to know the name of the app but may not have a direct link to it.